904 rebuild & converter recommendations

B&M is old technology as far as their shift improver technology goes. The Trans-go kits are light years ahead of them. They cost about twice as much but as the old saying goes "You gets what you pays for". The thing is not only do you get a better shift quality but your trans lasts longer due to less overlap during shifts. They address many shortcoming areas that most shift improver kits don't. Now the B&M friction plates may be good quality, I'm not really sure what they use. At the power level your talking about making you really only need good quality stock friction plates. If I were you I'd check with Chris at Andrews racing transmissions to see what he would recommend. He's real sharp. Here's the website. http://www.andrewsracingtrans.com/Transmissions/727/index.html
Another place I've ordered from with excellent results is Hensley's Performance.
http://hensleyperformance.com/index.php?type=1e
A mopar performance converter will probably do you just fine at your power level also. I've used them with good results on applications up to 400 HP. They have 3 stall sizes to match to your engine combo.